1. Field of the Invention
This invention relates to an image data coding apparatus and to a method and program for controlling the operation thereof.
2. Description of the Related Art
In comparison with the JPEG (Joint Photographic Experts Group) standard, the JPEG 2000 standard produces little noise even while raising the compression ratio. According to the JPEG 2000 standard, coding referred to as “EBCOT” (Embedded Block Coding with Optimized Truncation) is carried out after implementation of a wavelet transform (Non-Patent Document 1). Further, in coding such as provided by JPEG 2000, portions of code streams are discarded in such a manner that the overall amount of code will take on a target amount (Patent Document 1); computation such as a distortion slope for rate control is performed and rate control is carried out by discarding codes (Patent Document 2); the size of a code block, which is a unit of coding, is adjusted (Patent Document 3); compressed code data is re-compressed efficiently (Patent Document 4); and coding is performed at a high image quality (Patent Document 5).
[Patent Document 1]: Japanese Patent Application Laid-Open No. 2005-192087
[Patent Document 2]: Japanese Patent Application Laid-Open No. 2006-287487
[Patent Document 3]: Japanese Patent Application Laid-Open No. 2010-213059
[Patent Document 4]: Japanese Patent Application Laid-Open No. 2004-88164
[Patent Document 5]: Japanese Patent Application Laid-Open No. 2003-244443
[Non-Patent Document 1]: J. Li and S. Lei, “An embedded still image coder with rate-distortion optimization”, SPIE: Visual Communication and Image Processing, volume 3309, pp. 36-47, San Jose, Calif., January 1998
However, the technique set forth in Non-Patent Document 1 cannot adjust the amount of code finely and often image quality varies greatly from image to image. Further, image quality cannot be adjusted finely using the techniques described in Patent Documents 1 to 5.